When packaged items such as cigarettes, boxes of throat lozengers, packages of candies and the like, are packaged in accordance with the prior art, such packages are transported through a system wherein first the package is formed or folded to receive the cigarettes, candy, etc., secondly the packages are filled with the foregoing items, thirdly each package is wrapped in cellophane or plastic that is sealable material, and finally the packages are moved to a heating station or a sealing station whereat the sealable material is heated and pressed so that it seals the package to keep moisture thereout. In the prior art the heat station has been composed of a pair of heavy rigid metal blocks, serving as the heat transfer members and within each of these blocks there is located a heating element and a thermocouple.
The heat transfer blocks are disposed so that when a package is carried through the heating station the ends of the package rub against the heat transfer blocks and thus heat is transferred to the cellophane or plastic material so that these ends of the package heat up and are pressed together to become sealed. Such prior art heating stations have had a number of undesirable characteristics.
For instance, the heat transfer surface presented by the heated block of metal in the prior art is rigid and does not "follow" contours of the package, but instead the package must conform to the surface of heavy metal blocks. If a package should be shorter than the specified length or desired length the package is very often not properly sealed because heat and pressure have not been adequately supplied to the sealable material. On the other hand, if the package is longer than the desired specification the package ends are very often torn with the heavy rubbing against the heavy metal blocks. In addition as the work surface of the heavy metal blocks wear, (from the rubbing of the packages thereagainst), the surfaces of the heat transfer blocks may become uneven and the heat applied to the package becomes uneven leaving unsealed portions. Further, in addition, such heavy mass heating stations have inherent problems because of their high thermal inertia. The high thermal inertia characteristic has been a major factor in improperly heating packages at the beginning of a package sealing run and/or overheating such packages at the end of the excursion through the heat station.
To better understand the foregoing infirmity in the prior art devices, it should be understood that in order to seal the material which is to be sealed, that material should be heated to a point where it is partially "melted", or tacky, or adhesible, or fusible. The partially melted material layers are then pressed together and in effect fuse into one another to form, upon cooling, a seal. The task is to render the material in the fusible state by the proper amount of heat without destroying the material by too much heat. It should be borne in mind that the material, which is to be sealed, is wrapped around a package and that package acts as a heat sink. The package conducts heat away from the source. It follows that when a "cold" package first enters the heat station it acts to conduct heat from the source more readily than it conducts heat further along the excursion through the heat station. Accordingly the amount of heat which is present, (in the layers to be adhesed, or fused, at the beginning of the excursion through the heat station), is relatively small when compared to the heat available at the initial position of the heat station. If we consider the profile of the heat present, in the material which is to be sealed, as that material travels through the heat station we find that it is not a flat profile, as would be desirable with prior art heating station equipment. Instead the profile is a ramp shaped profile, which rises (in the amount of heat present) as the material moves through the heating station. The material which is to be sealed must be rendered partially melting within a thermal window. If the applied heat is too great the material is destroyed and if the applied heat is too little the material will not become adhesable or fusible. The upper and lower limits of the ramp profile described above must fit within the thermal window and these constraints have given rise to problems in the prior art. The solution does not lie in providing a higher heat to overcome the initial "cold" state problem with prior art equipment because with such equipment the "heat present", at the end of the excursion through the heat station, is destructive, i.e. the ramp profile dictates that the high end is beyond the limits of the thermal window. In the prior art the problem has been dealt with by extending the heat exposure time, by either extending the length of the heat station (thereby providing a longer heat transfer period) or by transporting the packages at a relatively slow rate.
In addition because in the prior art the packages rub against the surface of the heat transfer means without having such heat transfer means "give", there resulted, very often, a tearing of the package.
The present heating station is formed to overcome the problems inherent in an inflexible, heavy mass heat transfer means.